The present invention relates to polyurea-polyurethane acrylate polymer dispersions; their method of preparation and their use in coating and molding applications.
It has been known heretofore that the utilization of acrylate terminated urethane polymers in coating and molding compositions results in exceptional coating performance properties such as, for example, a unique combination of hardness and flexibility, abrasion resistance, solvent resistance, good application and adhesion properties and good final film appearance. Moreover, it has also been generally known that the presence of urea groups in polyurethane polymers further adds to the already excellent properties described above, for example, impact resistance, tear resistance, thermal stability and enhancement of the combination of hardness and flexibility. However, whereas, it is predominantly desirable to introduce urea groups into a urethane polymer system, depending upon the mode of introduction of these groups, they can result in disadvantageous properties in the final polymer.
Usually, urea-linked urethane polymers are formed by the use of an amine functional group-containing compound at the urea-forming step. For example, U.S. Pat. No. 4,097,439 discloses a process in which a diisocyanate is reacted first with a diol to form an isocyanate-terminated urethane followed by chain extension with a diamine and end-capping with hydroxyl-containing acrylate to form a urethane-urea acrylate polymer. German Pat. No. 2,404,239 is also directed to a polyurethane-polyurea resin formed from the reaction of a polyisocyanate with a polyol to form a polyurethane prepolymer which contains isocyanate groups, and then reacting this prepolymer with polyamine to form the resin product. Using amine-containing compounds in this manner as a device to introduce urea groups into a polymer chain has two significant effects. First the resultant polymer is prepared as a solution polymer and second there are adverse effects on the rheological properties, namely viscosity and thixotropy are markedly increased. This poses practical difficulties in coating and molding compositions such as Injection Molding wherein the molding composition is pumped from a storage receptacle to the molding machines. In areas of the pumping system where shearing forces are minimal, the composition tends to set up gel networks and solidify thus clogging the system and resulting in equipment malfunction and work delays. This phenomenom is further intensified with the use of aromatic polyisocyanates and/or ethylenically unsaturated monomeric diluents such as styrene and methyl methacrylate. There is therefore a need to produce a terminal ethylenically unsaturated urea-urethane polymer which has all of the beneficial properties described above but without the attendant rheological drawbacks.
In addition to the prior art mentioned above dealing with solution polymers, the article by Spitler and Lindsey, "PHD Polyols, A New Class of PUR Raw Materials", Journal of Cellular Plastics, January/February 1981, pages 43-50, discloses polyol dispersions which consist of particles of polyurea dispersed in a polyether polyol, the polyurea formed from the reaction of a polyisocyanate with a polyamine. Urea-urethane polyol is formed as a result of some polyol reacting with polyisocyanate followed by reaction with polyamine. These polyurea-urethane polyol dispersions, however, do not contain ethylenic unsaturation.